This invention relates to home security systems and more particularly to a home security system that provides for using the telephone company lines in a neighbor's home to send out messages for emergency services in the event that telephone company lines for the protected home have been cut by an intruder.
It is well known to provide a security system in a home where when a sensor detects that a door or window in the home has been opened by an intruder a signal will be conveyed to an alarm panel in the home causing an automatic telephone communicator (ATC) to seize the telephone company lines leading out of the home and send a message to a central station advising of the intrusion.
The problem with such a conventional security system is that when an intruder intends to break into a home he may first cut the telephone company lines connected to the telephone in the home thereby preventing the automatic telephone communicator in the home from sending out a message through the telephone for emergency assistance.
Now it is well known that all the homes in a particular neighborhood are serviced by a.c. supply lines connected to a common secondary winding of a power transformer. As a result, when a high frequency electrical signal is impressed on the outlet of the a.c. supply lines provided in one of the homes, these signals are transmitted along the a.c. supply lines to outlets provided in each of the other homes in the neighborhood.
Thus, in accordance with the present invention, in addition to the conventional security system in a protected home, a line-cut monitor is provided which is connected across the telephone company lines extending into the protected home and a pulse width modulator (PWM) transmitter is provided which is coupled to the a.c. supply in the protected home. Thus, in the event that the telephone company lines outside the protected home are cut, the PWM transmitter responds to a signal received from the alarm panel of the conventional security system and/or emergency panic buttons in the protected home and provides for transmitting this data in the form of modulated high frequency signals over the a.c. supply lines to a PWM receiver provided in a selected one of the neighbor's homes in the neighborhood. This data upon being received in the selected neighbor's home is utilized to activate an automatic telephone communicator (ATC) therein which seizes the telephone company lines connected to the telephone in the selected neighbor's home and sends out a prerecorded or coded message indicating the nature of the emergency to the central station.
Accordingly, one of the objects of the present invention is to provide a security system for a protected home that makes use of a neighbor's telephone company lines to send signals regarding emergencies to a central station in the event the telephone company lines at the protected home have been cut by an intruder.
Another object of the present invention is to provide for sending information to a central station as to whether a security system at a protected home is armed or unarmed so that the likelihood of whether a burglary is in progress can be more readily determined by an operator at the central station.
Yet another object of the present invention is to provide a conflict avoidance circuit coupled to a PWM transmitter in a protected home which prevents the PWM transmitter from impressing high frequency signals on the a.c. supply lines in the neighborhood until the conflict avoidance circuit detects the absence of any high frequency signals on the a.c. supply lines.
These and other objects and features of the present invention will be apparent through a consideration of the following description when viewed in the light of the accompanying drawings which show an exemplary schematic diagram of a preferred embodiment of the invention.